NRT1/PTR family (NPF), subfamily 1 and 2 of the Major Facilitator Superfamily of transporters
The plant Nitrate transporter/Peptide transporter (NRT1/PTR) family (NPF) is related to the POT (proton-coupled oligopeptide transporter), Peptide transporter (PepT/PTR), or Solute Carrier 15 (SLC15) family in animals. In contrast to related animal and bacterial counterparts, the plant proteins transport a wide variety of substrates including nitrate, peptides, amino acids, dicarboxylates, glucosinolates, as well as the plant hormones indole-3-acetic acid (IAA) and abscisic acid (ABA). A recent study identified eight subfamilies within this family, named NPF1-NPF8. NPF1 includes Medicago truncatula LATD/NIP, now named MtNPF1.7, which is a high-affinity nitrate transporter and is involved in nodulation and root architecture. NPF2 members are well-established nitrate and glucosinolate transporters, including Arabidopsis nitrate influx and efflux transporters with varied tissue and developmental specificity. Examples are AtNPF2.7, which is expressed in the cortex of mature roots, and AtNPF2.9, which is expressed in root companion cells where it is involved in phloem loading. NPF1/2 belongs to the Major Facilitator Superfamily (MFS) of membrane transport proteins, which are thought to function through a single substrate binding site, alternating-access mechanism involving a rocker-switch type of movement.
Feature 1:putative chemical substrate binding pocket [chemical binding site]
Evidence:
Comment:based on the structures of MFS transporters with bound substrates, substrate analogs, and/or inhibitors
Comment:since MFS proteins facilitate the transport of many different substrates including ions, sugar phosphates, drugs, neurotransmitters, nucleosides, amino acids, and peptides, the residues involved in substrate binding may not be strictly conserved among superfamily members
Comment:the substrate binding site or translocation pore has access to both sides of the membrane in an alternating fashion through a conformational change of the MFS transporter
Comment:NRT1/PTR family proteins transport a wide variety of substrates including nitrate, peptides, amino acids, dicarboxylates, glucosinolates, as well as the plant hormones indole-3-acetic acid (IAA) and abscisic acid (ABA).
Jiyao W et al.(2023). "The conserved domain database in 2023.",